Systems for transmitting rather low levels of power in the form of electromagnetic energy from one location to another have been extensively utilized such as in radio, TV and radar systems. These systems have also been proposed for much higher levels of power transfer between ground station and spacecraft, ground station and aircraft, and ground station and ground station. However, one problem inherent in such systems, especially as microwave beam power level increases, has been the potential hazard to life and property due to accidental intrusion into the power beam. The effects of high level microwave radiation (greater than 10 mW/cm.sup.2) on personel and property are known to be at least thermal for long term exposure and can result in dehydration, cataract formation, and, at very high intensities, "steam" explosions in trapped fluid situations. However, near perfect reflectors, such as aluminum sheets, are unaffected at least up to flux densities as high as kilowatts per square centimeter as in Cassegrainian antenna reflectors.
The effects of medium level microwave radiation (1-10 mW/cm.sup.2) on personnel are controversially theorized to be cardiovascular symptoms, white body cell shifts, temporary sterility, tension, nausea, brain arrhythmia and reduced sound perceptions. At lower levels (less than 1 mW/cm.sup.2) there are certain brain wave and central nervous system responses, selected chromosone breaks and behavior modifications attributed to microwave radiation. These levels may be encountered in sidelobes or grating lobes of beamed power antenna patterns. Since a person cannot see or hear an approaching microwave beam or high level sidelobe, a system to protect personel and property from the damaging effects of an encounter with a microwave power transmission beam is desirable. As the power of these systems increases, protection becomes more and more important. The present invention provides a microwave power transmission beam control apparatus and method which solves the safety problem associated with conventional microwave beam systems by diminishing the level of or by removing microwave radiation from the vincinity of an object intersecting the beam, thus providing a capability for increasing the power transmitted by microwave beams without increasing the hazard to personnel and property encountering such beams.